ABS resins are well known in the synthetic organic polymer art as a class of thermoplastics which offers excellent mechanical properties as well as good processability and chemical resistance. The general characteristics of ABS resins are described, for example, in "Modern Plastics Encyclopedia," McGraw-Hill, New York, N.Y., 1990, pp 90-91. ABS resins are co- or terpolymers which generally comprise a rigid styrene/acrylonitrile continuous phase in combination with a polybutadiene elastomer disperse phase. A graft copolymer in which small amounts of styrene and acrylonitrile are grafted onto butadiene chains may also be present to bridge the rigid phase and the elastomer phase and make them more compatible.
For purposes of the instant invention, an ABS resin is a thermoplastic, the chemical structure of which includes each of the following structural units, however combined: ##STR1## Further, a formulated ABS resin, for all purposes herein, comprises at least about 50 wt % ABS resin. The remainder of the formulated ABS resin comprises various monomeric or polymeric additives which modify the properties of the ABS resin. These additives include, for example, various impact modifiers, stabilizers, processing aids, pigments, flame retardants, synergists, etc. They can be incorporated into the ABS resin in various ways.
Incorporation of the various additives is not a trivial matter, and the properties of the formulated ABS resin can be affected by the manner in which it is done. When the additives are solids, dry-blending can be employed. For example, the solids can be mixed and heated to soften and homogenize the mass, which can then be sheeted, chopped, and pelletized.
A flame retardant, such as a halogenated organic compound, is often incorporated into a formulated ABS resin so as to constitute as much as about 25-30 wt % of the formulation. Such incorporation can adversely affect the properties, other than the flammability, of the formulated ABS resin. For example, a flame retardant having a high melting point range, such as decabromodiphenylethane, or decabromodiphenyl oxide will have a filler type effect on the ABS resin formulation, whereas a flame retardant having a lower melting point range will have a plasticizer effect on the formulation. Because of the effect flame retardants have on articles containing such ABS resin formulations, improvements in such formulations and formulation techniques are highly desirable and of significant commercial importance.